STUDIES OF SELF-FIELD AC LOSSES IN PBBI-2223 AG-SHEATHED TAPES

Self-field AC losses in PbBi-2223 Ag sheathed tapes were measured at d ifferent temperatures and frequencies using a lock-in amplifier and a Rogowski coil. For J<J(c), the loss component E'(J) of the surface ele ctric field showed a functional behaviour similar to fJ(2)/J(ci), wher e the induced current J(ci) is a function of dB/dt rather than a const ant as in the critical state. This observation suggests that, although the critical state may not be valid due to flux creep, the ac losses in this region are still magnetic in nature, due to a hysteretic stead y-state characterised by J(ci)=J(ci)(dB/dt). For J>J(c), the E'(J) cha racteristics coverage rapidly to a frequency independent function, as the losses become dominated by a resistive mechanism such as flux flow .